If you’ve grown citrus in southern California, you may have experienced damage from the citrus leafminer. It is the only mining pest that commonly attacks the leaves of citrus and closely related trees (kumquat and calamondin). Mines within the leaves appear wrinkled with a shallow, serpentine tunnels on the front or backside of under the surface of the leaf.
The pest, Phyllocnistis citrella, “was not found in California until 2000 when it was first detected in Imperial County,” according to CU IPM. Since then it has moved to infest citrus plants in the majority of Southern California counties.
The citrus leafminer is unlikely to attack adult trees unless there is a heavy population of the pest. They do not like older, hardened-off leaves but may resort to new growth on adult trees if no young trees are available.
Stages of Citrus Leafminer
Four stages identify the life cycle of the Citrus leafminer. These are egg, larval, pupal, and adult moth stages. Adults only live a week or two. Mating when they emerge from the rolled leaf, the female lays single eggs on the underside of young leaves, where the process repeats itself. A preferred spot for depositing the eggs is along a midvein on new, flush growth. This pest prefers a young tree on which to deposit eggs.
Identifying the Pest
The adult leafminer is less than ¼ inch long, with white iridescent forewings with brown markings, while the hind wings and body are white. Long fringe scales extend from the hindwing margins. Adults live a week or two, giving the female moth numerous opportunities to lay eggs after emitting a sex pheromone to attract males.
How Leafminer Damage Begins
When the egg hatches, larvae begin eating the leaf near where the egg was left. They quickly eat their way inside the leaf, creating mines that are hard to see in the beginning. Eventually, they work through the interior of the leaf, leaving a dark, unsightly trail of frass (feces) that is more detectable to the naked eye. This indicates movement of the larvae. After molting four times, the larvae move on to roll themselves into a leaf. Inside the leaf, they move to the pre-pupal stage which lasts one to three weeks, creating extensive leaf damage and preparing to emerge as an adult.
While damage from this pest may make young trees stop growing temporarily, most sources agree that sprays do not reach those inside the leaf and may also kill natural enemies of the leafminer. Traps are available for the adult moths. Traps are not meant to contain the moths, but for identification purposes before you begin treatment. Don’t confuse the citrus leafminer with citrus peelminer that tunnels into stems and fruit.
Treatment of Citrus Leafminer
Wasps of Cirrospilus and Pnigalio species are natural predators of the citrus leafminer. They lay eggs on top of the eggs deposited by the leafminer moth that eat the larva once hatched. Use good physical controls, such as pruning water sprouts and suckers from your citrus trees. Avoid nitrogen fertilizer in summer and fall as it increases leaf flushes. Natural predators will find the leafminer and decrease their population.
Remove damaged leaves to reduce the population of this insect. However, this will encourage new growth, so monitor and repeatedly remove infected young leaves until the ratio of healthy leaves to damaged ones changes. If diligent, over time, there will be little to no more infected leaves. Prune live limbs just once a year to keep flushes short and uniform.
Citrus growing areas outside the U.S. with established infestations of the leafminer, find that natural predators arrive within the first or second year and effectively control the pest population. UC IPM advises, “Do not use broad-spectrum insecticides and avoid other practices that disrupt natural enemies whenever possible.”
A healthy citrus tree is the best defense against the citrus leafminer and other pests. Start by planting a healthy, high quality citrus tree from the trusted professionals at Paradise Nursery. Keep it healthy by following the care instructions we provide. If questions arise, feel free to contact us. Our experienced staff is available to consult, design, install, and manage your landscape and home orchard.